Multilayer ultrasonic transducer array including very thin layer of transducer elements

Abstract

An ultrasonic transducer array having a plurality of transducer elements, at least some of which have multiple piezoelectric and electrode layers. The resonant frequency of the transducer elements may range from 500 kHz to 300 MHz or more. A single array may have transducer elements of different resonant frequencies, and the array may be sparsely populated. Highest frequencies are typically obtained when the piezoelectric layers are made from vapor deposited PZT in accordance with a disclosed deposition process. The array may have a 1-D configuration, 1.5-D or 2-D, configuration. The array may be positioned in a probe.

What is claimed is: 
     
       1. An ultrasonic transducer array comprising: a. at least one layer of PZT having a thickness of less than 50 microns; and   b. an electrical conductor assembly attached to said at least one layer of PZT.   
     
     
       2. An ultrasonic transducer array according to claim 1, wherein said at least one layer of PZT comprises two or more layers of PZT and said electrical conductor assembly comprises first and second electrodes attached to said layers. 
     
     
       3. An ultrasonic transducer array according to claim 1, wherein said at least one layer of PZT has a thickness of no more than 10 microns. 
     
     
       4. An ultrasonic transducer array comprising: a. a plurality of piezoelectric layers;   b. a plurality of electrode layers interposed between said plurality of piezoelectric layers; and   c. wherein said ultrasonic transducer array is capable of operating at resonant frequencies in excess of 5 MHz with an electrical impedance of less than 100 Ohms.   
     
     
       5. An ultrasonic transducer array according to claim 4, wherein at least one of said piezoelectric layers has a thickness of less than 50 microns. 
     
     
       6. An ultrasonic transducer array according to claim 4, wherein said plurality of piezoelectric layers are made from PZT. 
     
     
       7. An ultrasonic transducer array according to claim 4, wherein said ultrasonic transducer array is capable of operating at resonant frequencies in excess of 10 MHz. 
     
     
       8. An ultrasonic transducer array according to claim 4, further comprising: d. a first electrical conductor assembly attached to first ones of said plurality of electrode layers; and   e. a second electrical conductor assembly attached to second ones of said plurality of electrode layers.   
     
     
       9. An ultrasonic transducer array according to claim 4, further comprising a substrate having a first surface, wherein said plurality of piezoelectric layers and said plurality of electrode layers are provided on said first surface. 
     
     
       10. An ultrasonic transducer array according to claim 9, wherein said first surface is planar. 
     
     
       11. An ultrasonic transducer array according to claim 9, wherein said first surface is non-planar. 
     
     
       12. An ultrasonic transducer array comprising: a. a plurality of ultrasonic transducer elements, each having: i. a plurality of piezoelectric layers;   ii. a plurality of first electrodes, each contacting at least one of said plurality of piezoelectric layers;   iii. a plurality of second electrodes, each contacting at least one of said plurality of piezoelectric layers;     b. a connector structure having: i. a plurality of first connectors attached to said plurality of first electrodes;   ii. a plurality of second connectors attached to said plurality of second electrodes; and     c. wherein at least some of said ultrasonic transducer elements contact one of said first connectors and two of said second connectors.   
     
     
       13. An ultrasonic transducer array according to claim 12, wherein said plurality of first connectors is electrically isolated from said second electrodes and said plurality of second connectors is electrically isolated from said first electrodes. 
     
     
       14. An ultrasonic transducer array according to claim 12, wherein said plurality of first connectors is electrically isolated from said plurality of second connectors. 
     
     
       15. An ultrasonic transducer array according to claim 12, wherein said plurality of piezoelectric layers are made from PZT. 
     
     
       16. An ultrasonic transducer array comprising: a. a plurality of adjacent ultrasonic transducer elements, each element having: i. a plurality of piezoelectric layers;   ii. a plurality of electrode layers;     b. a connector structure having a plurality of connectors connected to said plurality of electrode layers; and   c. wherein at least two of said ultrasonic transducer elements are separated only by one of said connectors.   
     
     
       17. An ultrasonic transducer array according to claim 16, wherein said at least two ultrasonic transducer elements physically contact said one connector separating said elements. 
     
     
       18. An ultrasonic transducer array according to claim 16, wherein said plurality of piezoelectric layers are made from PZT. 
     
     
       19. An ultrasonic transducer array according to claim 4, wherein said ultrasonic transducer array is capable of operating at resonant frequencies in excess of 15 MHz. 
     
     
       20. An ultrasonic transducer array according to claim 1, wherein said at least one layer of PZT has a thickness of less than 25 microns. 
     
     
       21. An ultrasonic transducer array comprising: a. a plurality of first ultrasonic transducer elements having a first resonant frequency, each element having two or more piezoelectric layers, and a first electrode assembly attached to said two or more piezoelectric layers;   b. a plurality of second ultrasonic transducer elements having a second resonant frequency, each element having two or more piezoelectric layers, and a second electrode assembly attached to said two or more piezoelectric layers; and   c. wherein said first and second resonant frequencies are different, and said plurality of first ultrasonic transducer elements are acoustically isolated from said plurality of second ultrasonic transducer elements.   
     
     
       22. An ultrasonic transducer array according to claim 21, wherein said first resonant frequency is less than 0.3 times the average of said first and second resonant frequencies and said second resonant frequency is more than 1.7 times the average of said first and second resonant frequencies. 
     
     
       23. An ultrasonic transducer array according to claim 19, wherein said piezoelectric layers in said first and second ultrasonic transducer elements are made from PZT. 
     
     
       24. An ultrasonic transducer array according to claim 19, wherein said first and second electrode assemblies are electrically isolated. 
     
     
       25. An ultrasonic transducer array according to claim 19, wherein said plurality of first ultrasonic transducer elements are optimized to transmit ultrasonic energy and said plurality of second ultrasonic transducer elements are optimized to receive ultrasonic energy. 
     
     
       26. An ultrasonic transducer array according to claim 19, further comprising a substrate having a first, non-planar, surface, wherein said pluralities of first and second ultrasonic transducer elements and said first and second electrode assemblies are positioned on said first surface. 
     
     
       27. An ultrasonic transducer array comprising: a. N×M transducer element regions, wherein N is the number of said regions as measured in a first direction and M is the number of said regions as measured in a second direction;   b. a plurality of ultrasonic transducer elements, each having one or more piezoelectric layers and an electrode assembly connected to said one or more piezoelectric layers; and   c. wherein X(N×M) of said transducer element regions contain one of said plurality of ultrasonic transducer elements, and X<1.   
     
     
       28. An ultrasonic transducer array according to claim 27, wherein X<0.5. 
     
     
       29. An ultrasonic transducer array according to claim 27, wherein X<0.25. 
     
     
       30. An ultrasonic transducer array according to claim 27, wherein said plurality of ultrasonic transducer elements comprises: a. a first group of ultrasonic transducer elements for transmitting ultrasonic energy; and   b. a second group of ultrasonic transducer elements for receiving ultrasonic energy.   
     
     
       31. An ultrasonic transducer array according to claim 27, wherein said plurality of ultrasonic transducer elements comprises: a. a first group of ultrasonic transducer elements having a first resonant frequency;   b. a second group of ultrasonic transducer elements having a second resonant frequency; and   c. wherein said first resonant frequency is different than said second resonant frequency.   
     
     
       32. An ultrasonic transducer array according to claim 27, wherein said plurality of ultrasonic transducer elements comprises: a. a first group of ultrasonic transducer elements, each having one piezoelectric layer;   b. a second group of ultrasonic transducer elements, each having two or more piezoelectric layers.   
     
     
       33. An ultrasonic transducer array according to claim 27, wherein said one or more piezoelectric layers are made from PZT. 
     
     
       34. An ultrasonic transducer array according to claim 27, wherein said plurality of ultrasonic transducer elements are randomly distributed in said transducer element regions. 
     
     
       35. An ultrasonic transducer array comprising a plurality of ultrasonic transducer elements, at least one of said elements having a resonant frequency greater than 10 MHz and three or more piezoelectric layers, said elements being arranged in a 1-D configuration, further wherein one or more of said elements has a length to width aspect ratio such that the length dimension is no more than five times the width dimension. 
     
     
       36. An ultrasonic transducer array according to claim 35, wherein said length dimension is substantially equal to said width dimension. 
     
     
       37. An ultrasonic transducer array according to claim 35, wherein said resonant frequency is greater than 15 MHz. 
     
     
       38. An ultrasonic transducer array having a plurality of multilayer transducer elements, each having height, width and length dimensions, wherein at least one of said width and length dimensions is less than 50 microns. 
     
     
       39. An ultrasonic transducer array according to claim 38, wherein at least one of said width and length dimensions does not exceed 25 microns. 
     
     
       40. An ultrasonic transducer array according to claim 38, wherein said width dimension times said length dimension does not exceed 0.0025 mm 2 . 
     
     
       41. An ultrasonic transducer array according to claim 38, wherein said width dimension times said length dimension does not exceed 0.000625 mm 2 . 
     
     
       42. An ultrasonic transducer array according to claim 38, wherein said length dimension is 1-5 times said width dimension. 
     
     
       43. An ultrasonic transducer array according to claim 38, wherein said elements are arranged in a 2-D array. 
     
     
       44. A method of making an ultrasonic transducer array comprising the steps of: a. providing a first electrode; and   b. vapor depositing a first PZT layer on said first electrode, said first PZT layer having a thickness of more than 5 microns.   
     
     
       45. A method according to claim 44, further comprising the steps of: a. providing a second electrode on said first PZT layer; and   b. vapor depositing a second PZT layer on said second electrode.   
     
     
       46. A method according to claim 45, further comprising the steps of: a. isolating first portions of said first electrode from second portions of said first electrode; and   b. providing a first connector attached to said first electrode.   
     
     
       47. A method according to claim 46, wherein said isolating step comprises the steps of: i. forming a kerf extending through said first electrode; and   ii. depositing an acoustically isolating material in said kerf.   
     
     
       48. A method according to claim 44, wherein said first PZT layer has a thickness of more than 10 microns. 
     
     
       49. A method of depositing PZT material comprising the steps of: a. providing a substrate;   b. vapor depositing PZT on said substrate at a rate of at least 0.5 microns per hour.   
     
     
       50. A method according to claim 49, wherein said step b comprises the steps of: i. providing a vapor deposition device;   ii. providing a target having at least one first portion made from zirconium and at least one second portion made from titanium, wherein the ratio of the surface area of said first portion to the surface area of said second portion ranges from 40% to 55%; and   iii. positioning said target in said vapor deposition device.   
     
     
       51. A method according to claim 49, wherein said PZT is deposited to a thickness of more than 5 microns. 
     
     
       52. A method according to claim 49, wherein said step b includes the steps of: i. providing a target in a vapor deposition device, said target comprising first portions made from zirconium, second portions made from titanium and third portions made from lead; and   ii. sputtering said first, second and third portions in an environment containing oxygen so as to cause lead oxide, zirconium oxide and titanium oxide to be deposited on said substrate.   
     
     
       53. A method of depositing PZT material comprising the steps of: a. providing a substrate;   b. vapor depositing PZT on said substrate to thickness of more than 5 microns.   
     
     
       54. A method according to claim 53, wherein said step b involves depositing said PZT to a thickness of more than 10 microns.